1. Field of the Invention
The present invention relates to a method for producing a surface emitting semiconductor device.
2. Description of the Related Art
A vertical cavity surface emitting laser (VCSEL), for example, includes an active layer, a distributed Bragg reflector (DBR), and a current-confinement layer disposed between the active layer and the DBR. The current-confinement layer has a high-resistance region so as to confine a current in a center region surrounding the high-resistance region. For example, U.S. Pat. No. 6,570,905 describes a VCSEL formed on a GaAs substrate. In the VCSEL, an AlGaAs layer having a high aluminum content of 90% or more is used as a current-confinement layer.
FIGS. 12 to 15 are cross-sectional views showing steps of producing such a VCSEL. First, as shown in FIG. 12, an n-type DBR 102, an active layer (multi quantum well (MQW) structure) 103, a spacer layer 110, a current-confinement layer 104, and a p-type DBR 105 are sequentially grown on an n-type GaAs substrate 101. The n-type DBR 102 includes low-refractive-index layers 102a composed of Al0.9Ga0.1As and high-refractive-index layers 102b composed of Al0.1Ga0.9As, the low-refractive-index layers 102a and the high-refractive-index layers 102b being alternately stacked. Similarly, the p-type DBR 105 includes low-refractive-index layers 105a composed of Al0.9Ga0.1As and high-refractive-index layers 105b composed of Al0.1Ga0.9As, the low-refractive-index layers 105a and the high-refractive-index layers 105b being alternately stacked. The current-confinement layer 104 is composed of, for example, Al0.96Ga0.04As.
Next, a dry etching process is performed on the p-type DBR 105 and the current-confinement layer 104 to form a mesa portion 106 shown in FIG. 13. Subsequently, as shown in FIG. 14, the current-confinement layer 104 of the mesa portion 106 is oxidized from the side face of the mesa portion 106 toward the inside thereof. Thus, an annular oxidized region (high-resistance region) 104a containing aluminum oxide is formed in the current-confinement layer 104. In this step, in the p-type DBR 105, the low-refractive-index layers 105a composed of Al0.9Ga0.1As having a relatively high aluminum content are also oxidized from the side face of the mesa portion 106 toward the inside thereof, simultaneously. As a result, oxidized regions 105c containing aluminum oxide are formed. Subsequently, as shown in FIG. 15, an insulating film 107 and electrodes 108 and 109 are formed, thus producing a VCSEL 100. The VCSEL 100 has the annular oxidized region (high-resistance region) 104a containing aluminum oxide in the current-confinement layer 104. A current is confined in the center region surrounding the high-resistance oxidized region 104a. 